Optical receivers are configured to receive optical signals which include modulated information streams, and to provide an electrical signal corresponding to the modulated information streams. The corresponding electrical signal can include threshold voltages which determine the value of the information, e.g. a logical “1” and “0” bit. Note, the information can be modulated in a variety of formats, such as on-off keying, multi-level coding, phase modulation, etc. Referring to FIG. 1, an eye diagram 10 illustrates a conventional mechanism for receiver threshold voltage determination of a receiver. Eye diagrams illustrate a pattern produced in the optical signal (and corresponding electrical signal) is synchronously observed over many bits, i.e. an overlay of all the bits transmitted. The eye diagram 10 is useful to illustrate deleterious effects, such as dispersion, noise, non-linear effects, etc., associated with optical transmission systems.
The eye diagram 10 is a graph of decision level, illustrated in percent, versus time. The decision level can correspond to a voltage level in the electrical signal, and the time corresponds to a unit interval (UI) from 0 to 1. The UI represents a time interval over which the receiver receives one symbol of information. In the exemplary eye diagram 10, there is a high optical power level 12 representing a logical “1” level and a low optical power level 14 representing a logical “0”. The eye diagram 10 includes a decision threshold 16 above which represents the “1” level and below which represents the “0” level. In practice, the high optical power level 12 and the low optical power level 14 are impacted due to dispersion, noise, and non-linear effects. For example, dispersion lowers the high optical power level 12 and raises the low optical power level 14, and noise and non-linear effects can expand the levels 12, 14. Accordingly, the receiver may experience errors based on these effects.
Pluggable optical transceivers utilize an optical receiver to receive an optical signal from a corresponding optical transmitter. Pluggable optical transceivers are defined through multi-source agreements (MSAs). MSAs are agreements for specifications of pluggable transceivers agreed to by two or more vendors and promulgated for other vendors and network operators to utilize. MSAs allow other vendors to design transceivers to the same specifications reducing risk for vendors and operators, increasing flexibility, and accelerating the introduction of new technology. Exemplary MSAs include XFP, XPAK, XENPAK, X2, XFP-E, SFP, SFP+, 300-pin, and the like. Additionally, new MSAs are emerging to address new services and advanced technology. Each MSA defines the transceiver's mechanical characteristics, management interfaces, electrical characteristics, optical characteristics, and thermal requirements. Because of MSA specifications, MSA-compliant pluggable transceivers are standardized among equipment vendors and network operators to support multiple sources for pluggable transceivers and interoperability. As such, MSA-compliant pluggable transceivers have become the dominant form of optical transmitters and receivers in the industry.
Advantageously, MSA-compliant pluggable transceivers ensure engineering re-use and compatibility between various applications and the physical media dependent transceivers. Further, equipment vendors realize streamlined manufacturing and inventory control by removing wavelength specific decisions from the manufacturing process. For example, all line cards are manufactured the same, and the pluggable transceiver module with the desired wavelength (e.g. 850 nm, 1310 nm, 1550 nm, coarse wave division multiplexed (CWDM), dense wave division multiplexed (DWDM), etc.) is plugged in as a function of the specific application or development configuration. Network operators and service providers have adopted pluggable transceivers to reduce sparing costs. Further, significant cost reductions are realized by MSA standardization of pluggable transceivers because of multiple independent manufacturing sources.
The MSA specifications tightly define the mechanical characteristics, management interfaces, electrical characteristics, optical characteristics, and thermal requirements of pluggable transceivers. Advantageously, this enables interoperability among equipment vendors of pluggable transceivers, i.e. any MSA-compatible pluggable transceiver can be used in any host system designed to the MSA specification; however, these tightly defined characteristics limit the performance of pluggable transceivers since the MSA specifications were designed to maximize density and minimize cost, and not to provide advanced optical performance. Disadvantageously, conventional pluggable optical transceivers do not provide advanced optical layer operations, administration, maintenance, and provisioning (OAM&P) and forward error correction (FEC). Accordingly, these conventional pluggable optical transceivers do not include receiver threshold optimization algorithms.
Conventional techniques exist in the art to adjust the decision threshold 16 to improve receiver performance. For example, these techniques can adjust the decision level of the decision threshold 16 based upon a plurality of parameters and calculations. However, such techniques are complex and often require external communication from the receiver, such as to receive the plurality of parameters and calculations. It would be useful to implement a receiver optimization threshold loop which can provide self-contained automatic adjustment in a compact module, such as a pluggable optical transceiver. Due to the low-cost, high-density, and widespread deployment of pluggable transceivers, both equipment vendors and network operators recognize a need to extend the benefits of pluggable transceivers to metro, regional and core network applications to enable carrier-grade wavelength division multiplexed (WDM) transport without the need for additional equipment such as optical transponders or additional circuitry performance enhancements. Such a need also must preserve the MSA mechanical characteristics, management interfaces, electrical characteristics, optical characteristics, and thermal requirements to maintain interoperability with existing host systems.